AND PLANTS 85 



range he would be unable to predict the result of any 

 new measurement, however often and however carefully 

 he had measured his triangle before. 



If I tried to show you the results of measuring the 

 three angles of a triangle a great many times, I should 

 probably tire you very soon : I shall therefore only ask 

 you to look at measurements of a single angle, so that 

 you may realize the sort of approximation to a constant 

 result which skilled observers can reach when they make 

 repeated measurements of what seems to be a constant 

 angle. 



Some of you know the Radcliffe Observatory in the 

 Woodstock Road. In it there is a telescope, with which 

 important observations have been made, and astronomers 

 all over the world are anxious to know the position of 

 this telescope on the earth's surface as exactly as possible, 

 in order to compare their own observations with those 

 made through it. Accordingly, successive observers have 

 determined the latitude and longitude of that telescope 

 with great care. You know what the latitude of that 

 telescope is. It is the angle between two imaginary 

 straight lines, which start from the centre of the Earth, 

 and come to the surface in the meridian of Oxford, one 

 coming out at the Equator, and the other through the 

 telescope ; so that determinations of the latitude of that 

 telescope are attempts to measure an angle. In the 

 Nautical Almanac, and in various other publications, the 

 latitude of the Radcliffe telescope is given, together with 

 that of many other instruments ; but if you look at these 

 various publications, you will find the value given for the 

 latitude of the Radcliffe telescope is not always the same. 



Between 1840 and 1887 the Radcliffe observers pub- 

 lished their own estimates of their latitude, with this 

 result : 



